There is a web form to paste your code into and it will return your converted AS3 code (check it here).
There is also an command line exe in the zip file
I’m not very good at command line, so for your (and mine) convenience I will explain how to get the exe to work with a .BAT file (I work on a PC so the example only works on PC).

Download the zip file and extract it somewhere on your computer. In my case C:\tmp\convert
I’ve created to folders in the convert folderC:\tmp\convert\input
C:\tmp\convert\output
and in the input folder I copied all the classes I’ve ever written.

Now create a file with a .BAT extension (in my case convert.bat) and it doesn’t matter where you put it, but I put it next to the convertas2as3.exe in C:\tmp\convert folder.

Open the file you just created and paste this in there:
pause
C:\tmp\convert\convertas2as3.exe -input "C:\tmp\convert\input" -output "C:\tmp\convert\output"

or adjust the path to the files you want to convert
save the file and open the .BAT file (in my case convert.bat) and all your classes you ever have written are converted to AS3…

Well as good as it get’s: it’s not 100 percent converted to AS3 but it helps you with most of your code, and helps you on your way to find the correct code.

example
take the code I translated in the previous post but now in a class file: